There are many types of foam used to make shoes, here we are going to review the types of foam found in the uppers of shoes. Generally, foam is divided into two types, “Open Cell” and “Closed Cell” foam. Open cell is exactly what it sounds like, the plastic compound that makes up the foam cells is open, letting air and water free to enter and exit the foam just like a dishwashing sponge. Closed-cell foam is exactly the opposite, individual cells are closed or sealed not allowing the foams internal gas to escape.
Open-cell foam is generally softer, these foams are made of Polyurethane plastic. One common type of this foam that is commonly used and referenced is “KF or KFF” foam. Open-cell foam is available in different densities and in almost any thickness and color. Open-cell foam is used in the tongues and collars of shoes and thin sheets of PU foam are used to back fabric in most shoe uppers. PU foam allows the stitches to sink in and gives mesh some extra support while reducing wrinkles.
Reticulated foam is the most open style of foam. This type is often used for ventilation features.
Closed-cell foam is generally denser. Midsoles of shoes are all made from closed cell foam. Midsole foam is covered the article Outsole Design. Common Closed cell foams include EVA (ethyl vinyl acetate), PE (Polyethylene), SBR Styrene butadiene rubber), PU (Polyurethane), Latex, and Neoprene, each with their own properties. EVA foam is used for backing mesh materials, and 2mm sheet EVA will make the fabric waterproof. Neoprene and SBR are used when elastic properties required, while Latex is common for collar linings. PE foam is very light but not so durable, making its use more limited.